In a continuous Czochralski (CZ) crystal growth process, the melt is supplemented or recharged as the crystal is growing. This is in contrast with batch recharge wherein the melt is recharged after the melt is depleted by a completion of a crystal growing process. In either case the melt can be supplemented either with solid feedstock or molten feedstock.
In contrast to batch recharge, there are advantages of a continuous Czochralski process for growing crystal silicon ingots. The melt height remains substantially constant and therefore the growth conditions at the melt-crystal interface can be maintained more uniformly for optimal crystal growth. The cycle time may also be reduced because the melt conditions are not suddenly changed by the addition of a large quantity of feedstock.
A conventional weir arrangement in a conventional continuous crystal growth crucible is shown in FIG. 1. In the conventional Czochralski system, a crucible 100 holds a quantity of molten silicon 102 in which a single crystal ingot 104 is grown and pulled in a vertical direction indicated by arrow 105 from a crystal/melt interface 106. A weir 108, typically shaped as a cylinder is positioned on the floor of the crucible 100 and extends vertically above the melt as shown. The weir 108 defines an inner growth region 110 and an outer melt supplementing region 112. Subsurface passageways 114 connect the first or melt supplementing region 112 with the inner growth region 110.
A heat shield 116 is conical in shape and extends downwardly at an angle to create an annular opening disposed about the growing crystal or ingot 104 to permit the growing ingot to radiate its latent heat of solidification and thermal flux from the melt. The top of the heat shield 116 has a first diameter much wider than the diameter forming the annular opening around the ingot 104. The top of the heat shield 116 is supportably held by an insulating lid or insulation pack. The insulating lid is omitted from the drawing for the sake of simplicity. A flow of an inert gas, such as Argon, is typically provided along the length of the growing crystal as indicated at 117.
A feed supply 118 provides a quantity of silicon feedstock to the melt supplement region 112 of the crucible 100. The silicon feedstock may be in the form of solid chunks of silicon feedstock provided directly to melt region 112. In either case, addition of feedstock to the melt region is often accompanied by particles of dust transported by aerostatic forces over the top of weir 108. The dust or unmelted silicon particles contaminate the growth region 110 and can become attached to the growing ingot 104, thereby causing it to lose its single silicon structure.
Although the conventional weir 108 arrangement of FIG. 1 may help to limit transmission of dust and un-melted particles of silicon by means of melt flowing from the melt supplementing region to the crystal growth region, it fails to address the problem of high erosion rates of the weir. As shown in FIG. 5, conventional quartz weir 108 is subjected to silicon monoxide and Argon gas. Argon gas is pumped over the liquid silicon to remove silicon monoxide gases and to reduce the concentration of oxygen incorporated in the grown crystal. The Argon gas and silicon monoxide gas are indicated by streamlines 500. A side effect of the gas flow is that the weir undergoes rapid erosion at the melt-gas contact line 119 due to surface kinetics and eventually is cut-through to the extent that it no longer functions as a sufficient barrier to the solid polysilicon. Such erosion poses a problem because it requires that the weirs be frequently replaced, causing downtime and increased cost for replacement.
While this conventional weir 108 arrangement may be adequate for preventing unmelted silicon from the melt supplementing region to reach the crystal growth region, the arrangement fails to address the problem of rapid erosion of the weir. This rapid erosion may increase the cost of the process and may decrease throughput by causing downtime to replace the weir.
This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.